Update onboarding, demo, and homepage

[JairusSW]

What changed

• document the actual CLI export-selection order
• show platform-specific commands for running compiled executables
• update and regenerate the Fibonacci terminal demo
• move the homepage navigation cards beneath the product overview and tighten the introductory copy

Why

The guide incorrectly described filename-based export selection, while standalone compilation of the library-style Fibonacci module requires an explicit --invoke fib. The homepage now leads with what Wago is before presenting navigation choices.

Validation

• npm run docs:check
• regenerated the VHS demo with deterministic humanized typing
• visually inspected representative GIF frames
• verified the standalone Fibonacci executable prints fib(30) = 832040